1. Field of the Invention
The present invention relates to a light-emitting device.
The present invention further relates to a method for manufacturing a light-emitting device.
2. Related Art
Organic light emitting devices (“OLEDs”), including both polymer and small-molecule OLEDs, are potential candidates for a great variety of virtual- and direct-view type displays, such as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators and the like. Unlike inorganic semiconductor light emitting devices, organic light emitting devices are generally simple and are relatively easy and inexpensive to fabricate. Also, OLEDs readily lend themselves to applications requiring a wide variety of colors and to applications that concern large-area devices.
OLEDs generate light when an electron and a hole combine in a light-emitting layer in the OLED to generate a photon. The percentage of combined electrons and holes that result in generation of a photon in the light-emitting layer is referred to as the “internal electroluminescence quantum efficiency.” The percentage of generated photons that are transmitted or “coupled” out of the device is referred to as the “external electroluminescence quantum efficiency” or the “out-coupling” efficiency of the device. Models predict that only about 20% or less of the generated photons are transmitted out of the device. It is believed that this is at least in part due to the fact that the generated photons are trapped within the OLED device by internal reflection at interfaces within the OLED, resulting in waveguiding of the photons within the OLED and absorption of the trapped photons by the OLED. Absorption can occur within any part of the OLED device, such as within an ITO anode layer or within the substrate. Internal reflection occurs where the refractive index of that particular part is greater than the refractive indices of the adjacent parts. These phenomena result in decreased external electroluminescence quantum efficiency and a reduction in the luminescence or brightness in directions extending outwardly from the surface of the device.
US 2003127973 describes an OLED that is provided with a composite barrier layer disposed over the active region and/or on a surface of the substrate. The composite barrier layer comprises an alternating series of one or more polymeric planarizing sublayers and one or more high-density sublayers. At least one of the polymeric planarizing sublayers has microparticles incorporated therein. This includes preferably the polymeric planarizing sublayer closest to the active region. The microparticles are effective to increase the out-coupling efficiency of the OLED. The microparticles are preferably comprised of a transparent material, preferably an inorganic material such as a metal, metal oxide, e.g., TiO2, or other ceramic material having a relatively high index of refraction, preferably, the microparticles will have an index of refraction of greater than about 1.7. The microparticles are preferably substantially smaller than the largest dimension of any active region or pixel in a display comprising an OLED device of the invention. The microparticles preferably will have a size greater than the wavelength λ, of light generated by the OLED. Thus, the microparticles will preferably have a particle size greater than about 0.4 μm-0.7 μm. The microparticles will preferably have a size in the range of from about 0.4 μm to about 10 μm or greater. The presence of the microparticles reduces the planarizing effect of the planarizing layer.
It is noted that US2009/302744 A1 discloses an OLED device and a manufacturing method thereof. Organic light emission diode elements are disposed on a substrate. On the substrate with the organic light emission diode elements, a sealant layer having a micro-lens portion is disposed, thereby shielding the organic light emission diode elements from external moisture and/or oxygen. The sealant layer is formed of a pre-composition that includes a liquid pre-polymer. In an embodiment the sealant layer is sandwiched between two auxiliary sealant layers. An auxiliary sealant layer can be one of a silicon oxide film and a silicon nitride, or a stacked layer thereof.
It is further noted that US2005 194896 A1 discloses light-emitting device with a light extraction layer formed by a transparent medium dispersed with a fine transparent substance whose refractive index differs from that of the transparent medium.